1.Make pastry; sift flour, icing sugar and salt into a large bowl. Coarsely grate the butter into the dry ingredients. Rub the butter into the flour mixture until it resembles coarse crumbs. Add the water and stir into a soft dough. Turn dough onto a bench and form into a thin disc. Wrap the dough in plastic wrap; refrigerate for 20-30 minutes or until firm enough to roll.
2.Meanwhile, make almond paste; process all the ingredients to a thick paste.
3.Preheat the oven to 180°C (160°C fan-forced). Chop the rhubarb into 5cm pieces and put into a bowl with the frozen raspberries and caster sugar; toss to coat.
4.Lightly dust a large sheet of baking paper with flour and roll the pastry out to form a rough circle approximately 30cm in diameter. Transfer the pastry on the baking paper to a large oven tray. Spread the almond paste in the centre of the pastry, leaving an 8cm border. Top with the rhubarb mixture. Lift the sides of the pastry up over the fruit and crimp in place.
5.Bake on the lower shelf of the oven for 45-50 minutes or until crisp and golden. Dust with icing sugar and serve with double cream or ice-cream, if desired.
Not suitable to freeze or microwave.Note